In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the ability to provide network access in a broad range of frequency bands. It is foreseen that evolving radio access technologies (RATs) likely include operation in very high frequency bands, for example in the range 4-100 GHz. Long Term Evolution (LTE) radio access typically uses multiple frequency bands from both low frequency bands (e.g. 700-900 MHz) and high frequency bands (e.g. 1000-3500 MHz). The available bandwidth is commonly more limited in the lower frequency bands compared to in the higher frequency bands and the very high frequency bands. It is common that a network operator is allowed to allocate resources in both low frequency bands and high frequency bands. Today, the low frequency bands are well suited for providing network coverage at high distances between serving radio access network node and served wireless device and in indoor environments (where network coverage is provided by outdoor network nodes) due to better propagation characteristics than high frequency bands, whilst high frequency bands provide network coverage at shorter distances but with higher capacity than low frequency bands due to the larger bandwidth.
Dual connectivity has been specified for LTE and can be used to aggregate data flows from multiple radio access nodes in order to increase bandwidth when scheduling data for a wireless device. Dual connectivity was introduced in LTE Release 12 for inter frequency deployments, i.e., where two network nodes operate on separate frequencies in independent manner. A wireless device in dual connectivity, according to LTE Release 12, maintains simultaneous connections to a Master evolved Node B (MeNB) and at least one Secondary evolved Node B (SeNB) node. As the name indicates, the MeNB terminates the control plane connection towards the served wireless device and thus acts as the controlling node of the wireless device. In addition to the MeNB, the wireless device may be connected to at least one SeNB for added user plane support. By letting the wireless device transmit and receive data to and from two eNBs (one MeNB and one SeNB) at the same time, peak bit rates in the network can be increased by utilizing both frequency layers. By splitting the data higher up in the protocol stack (when compared to carrier aggregation), non-ideal backhaul and independent scheduling in the network node is supported. Further, the control plane and the user plane can be separated between different network nodes where the MeNB is responsible for the control plane connectivity and the SeNB is responsible for the user plane connectivity. In this case, user plane data can thus be offloaded to the SeNB, whilst the control plane signalling in maintained by the MeNB.
One approach for securing the control plane connectivity is to use dual connectivity between low frequency bands and high frequency bands and targeting the control plane connectivity for the low frequency bands (i.e. making a separation of the control plane and the data plane as disclosed above). One issue with this approach is that the low frequency bands may be overloaded if this approach always is used. On the other hand, for comparatively small data transfers it can be unnecessary to set up a connection to a SeNB. Therefore it is also important to balance load between MeNB.
Hence, there is still a need for an improved load balancing between network nodes in a dual connectivity supported communications networks.